Sound negative for direct production of sounds



Jan. 22, 1935. I 'v R. SCHMIDT 1,988,812

' SOUND NEGATIVVE FOR DIRECT PRODUCTION OF SOUNDS v Filed July 28, 1932Hg. l

dens/)fr curve Patented Jan. A22, 1935 PATENT OFFICE soUNn NEGATIVE ronnmEc'r monoc- TIoN or soUNns Richard Schmidt, Dessau,

, udg-norte Germany Agfa Ansco Corporation, Binghamton, N. Y., acorporation of New York Application July 28, 1932, Serial No. 625,515

Germany August 1, 1931 1 Claim.

My present invention relates to the manufacture of photographicallyregistered sound records and more particularly to the manufacture ofsuch records produced according to the varying 5 density method.

One of its objects is to provide a process according to which soundnegatives are obtainable for direct use without their printing beingnecessary. Another object is the sound -negatives giving directly a truereproduction of the original sounds. Further objects will be seen fromthe detailed speciflcation following hereafter. Reference is made to theaccompanying drawing showing in Fig. 1 the density and in Fig. 2 thetransparency curve of a silver halide gelatin emulsion `well suited forthe production of such sound negatives.

I have found that by a suitable development sound negatives, producedaccording to the varying density method, are obtainable which give atruel or substantially true reproduction of the tonal values and whichmay be used for direct sound reproduction. Inorder to realize thisproblem development must be eifected in such a manner that the curve oftransparency, i. e. the curve determined by the values of -t (lightintensity multiplied by the time of exposure) as abscissa: and thetransparencies T as ordinates is approximately a straight line. Thedensity curve '80 which is intimately related to the transparency curveand of which the absciss are graduated in values of log -t (i-t=lightintensity multiplied with the time of exposure) and the ordinates invalues of density s should approach as nearly as possible a logarithmiccurve. That means that the curve should be very flat in the region ofweak blackenngs and very steep for the region of blackenings beginningwith densities s=0,5 to 0,6. In order to permit the registration of agreat intensity range the straight region of the transparency curveshould be as long as possible.

For this purpose a suitable silver halide emulsion must be selected andit has been found that the emulsions which are most suitable for thepresent invention are those that have hitherto been used for theproduction of aerial surveys. It is first necessary to make a record ofthe transparency curve of this emulsion in order to determine theintensity of light which must be used in making the sound record. Thevalue of the abscissa in the middle of the straight portion of thetransparency curve gives the intensity of light required. Afterexposure, the emulsion containing the sound recordis developed by meansof a lo-called depth developer, preferably with a developer such as isused for developing titles. Such' developers yield clean negativesshowing great contrasts.

As known, for the photographic registration of sounds there is used asource of light of which 5 in the varying density method, the intensityis changed in accordance with the sound waves to be registered. 'I'hatmeans according to the oscillations of the sound waves the intensity ofthe source of light varies around a mean value l0 which corresponds withthe light intensity when the sound recording apparatus is at rest. Thismean value is given the mean value of the absciss of the straight partof the transparency curve.

`For better understanding I will now describe 15 my invention withreference to the accompanying drawing.

In Fig. 1 there is shown a density curve of a `silver halide gelatinemulsion suited for the production of a sound negative for directreproduction of the original sounds. The values for tracing this curvehave been ascertained in an ultrashort-time sensitometer realizing theconditions usual in taking a'sound negative. In determining this curveone of the factors must be con- Astant, in the present case the time ofexposure is of the product log i-t chosen as the constant factor and hasbeen given about 1/ 22000 sec. the time used in taking a sound recordvarying generally in the range of 1/20000 sec. to l/30000 sec. and 30being determined by the speed at which the lxn is fed through theapparatus and the breadth of the slit. The change of intensity of thesource of light used for exposing the film was effected by interpositionof a blackened wedge. The exposed film, in the present case Aerochromlm"(Agfa), was developed for about 10 minutes in a developer as usual fortitle develop# ing. In the figure ab designates that part of the curvewhich is applicable for the production of sound negatives givingdirectly a true reproduction of the original sounds without thenecessity for aprinting process.

In Fig. 2 there is shown the transparency curve corresponding with thedensity curve shown in Fig. 1. In this curve the part marked cdcorresponds to the part ab of Fig. l and is useful for the purposes ofthe invention. It may be mentioned that the part applicable for theproduction of sound negatives according to this invention need not be anabsolute straight line.

A deviation of this condition is admissible so long as the limit givenby a distortion of the upper harmonics is not crossed. The mean value ofthe light intensity to be used in taking the sound record, that is theintensity of the source of light for exposing the lm when the recordingapparatus is in its rest position is given by the value of dcorresponding in Fig. 2 with the abscissa 54 (the intensity units arearbitrary).

My invention is not limited to the foregoing example or to the specicdetails given therein. Changes indetail may occur to those skilled inthe art and I contemplate as included within my invention all suchmodifications as fall within the scope of -the appended claims.

My invention is applicable to all kinds of cinematography concerned withsound recording, but it is of particular importance for amateurcinematography, working with vsubstandard ilm in which case for economyssake .no prints should be made. In the case of the reversal process, thesound record-after the simultaneous development of the picture and soundnegative is finished, is protected from further action of the treatingliquids by providing it, in known manner, with a protective layer,whereupon the picture record is reversed to the positive in theusualmanner. Then after removal of the protective layer, the soundrecord is fixed. However, the sound track may also be provided with' aprotective layer before beginning the treatment of the picture area andafter the pictures have been produced, the protection layer is removedand the sound record is developed and fixed in the manner abovedescribed.

What I claim is:-

'Ihe process of producing a sound negative adapted for directreproduction of the sound which comprises exposing a nlm of steepgradation to a source of light having its intensity varying with soundwaves .to be recorded, adjusting the intensity of the unmodulated sourceof light to the mean value of the absciss of the straight part of thetransparency curve if said film the absciss designating it (lightintensity multiplied by the time of exposure) wherein t has a constantvalue and substantially corresponds with the period of exposure used inrecording, and developing the exposed iilm to a steep gradation. l

RICHARD SCHMIDT.

